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Fusion, the power that drives the sun and stars, produces massive amounts of energy. Scientists here on Earth seek to replicate this process, which merges light elements in the form of hot, charged plasma composed of free electrons and atomic nuclei, to create a virtually inexhaustible supply of power to generate electricity in what may be called a “star in a jar.”

Fusion, the power that drives the sun and stars, produces massive amounts of energy. Scientists here on Earth seek to replicate this process, which merges light elements in the form of hot, charged plasma composed of free electrons and atomic nuclei, to create a virtually inexhaustible supply of power to generate electricity in what may be called a “star in a jar.”

A long-time puzzle in the effort to capture the power of fusion on Earth is how to lessen or eliminate a common instability that occurs in the plasma called edge localized modes (ELMs). Just as the sun releases enormous bursts of energy in the form of solar flares, so flare-like bursts of ELMs can slam into the walls of doughnut-shaped tokamaks that house fusion reactions, potentially damaging the walls of the reactor.

Ripples control bursts

To control these bursts, scientists disturb the plasma with small magnetic ripples called resonant magnetic perturbations (RMPs) that distort the smooth, doughnut shape of the plasma — releasing excess pressure that lessens or prevents ELMs from occurring. The hard part is producing just the right amount of this 3D distortion to eliminate the ELMs without triggering other instabilities and releasing too much energy that, in the worst case, can lead to a major disruption that terminates the plasma.